1. Field
This invention generally relates to a testing method for evaluating the mechanical properties of a fibrin clot and specifically relates to the use of a polyvinyl chloride (PVC)plastic film as a template for fibrin glue in the mechanical testing.
2. Background
Fibrin glue has been advocated since 1940 (Brennan, 1991). It is widely used in Europe and Japan, and is routinely administered in the U.S. at various centers as an unregulated surgical tissue adhesive (Matras, 1985). Several manufacturers are trying to market a FDA-approved product in the U.S. The benefits of using a tissue adhesive or a tissue sealant like fibrin glue include better patient care, reduced morbidity and mortality, and cost containment (Gibble and Ness, 1990).
Fibrin glue is a three dimensional gel network that results from the enzymatic transformation of soluble fibrinogen by thrombin in the presence of calcium (Marx and Blankenfeld, 1993). The fibrin monomers polymerize and are subsequently cross-linked covalently by activated Factor XIII. The fibrin clot consolidates and adheres to the site of application. The form and structure of fibrin clots are affected by a number of factors which in turn affect the mechanical properties of the fibrin glue (Burnouf-Radosevich, et al. 1990). One of the most important parameters is clot rigidity. Although several papers report the evaluation of shear strength resulting from different fibrinogen concentrations in vitro, a thorough study comparing shear and tensile strength has not been reported. Also, the influence of biochemical and environmental variables has not been previously described in detail.
Studies of fibrin glue have involved measuring the mechanical properties of the fibrin clot. The force required to break the fibrin clot has been used to study the bonding strength of fibrin glue (Duda et al. 1993; Sierra et al. 1992). Tensile strength is force required to break fibrin glue by trans-axial force (applied as the elongating force in the plane of the bond) and shear strength is force required to break fibrin glue along the longitudinal axis (applied parallel to the plane). (See FIG. 2.) The methods used in these studies entail mixing the components of the fibrin glue together and applying the glue between two pieces of substrate material. After the glue solidifies the mechanical properties of the fibrin clot can be tested.
The substrate material typically used in these tests is porcine or other animal skin. There are, however, problems encountered with using porcine (or other animal) skin, such as reproducibility of consistent skin templates, animal source and availability, and storage and stability. Concerns about the humane treatment of animals and minimizing animal testing of products have now lead to the discovery of a practical substitute for the use of porcine skin in the testing of fibrin glue products.